Putting Wilhelm Out of Business

You need to get [item=206449] and turn in the quest before the pages for this will spawn, it seems.

Plague Quarter:

• Credit to Drizzm for finding this one: As you come into Plague Quarter, turn left in the first room and find the corpse wagon. The Page ([item=206458]) blends in rather well but it's on the spiked/studded wheel at the front.
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• Credit again to Drizzm: After Noth, go to the green grate in the mushroom hallway. On top of the largest of the mushroom trio at the back of the grate (against the wall) is a Page ([item=206459]) that blends in very well to the mushroom's edge.
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• Right under the north portcullis in Loatheb's room sits another Page ([item=206460]).
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• One ([item=206461]?) is found on the platform where you jump down into Noth's room from the outer ring. When you get to the Loatheb bridge, jump down and run southward until you get to the Noth ledge. To get there, you could also swim through from another wing, but that's up to you.
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Arachnid Quarter:

• Another ([item=206451]) is in the column in the center of the first trash room of the Arachnid wing. There's a hole in the southeast side, and you can find it there.
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• After Faerlina on the way to Maexxna, while in the heavily-egged, green, cave-looking hallway, there's a spot where it continues into a small round to the south before heading into the constructed hallway slightly to the east/left. Hidden among the egg sacs and webbings on the left side of the rounded part is another Page ([item=206452]).
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• [item=206473] required. Adding one from Strath's comment (credit to them!) so the list is more complete: After you enter Maexxna's room in Arachnid wing, turn around and the point is right above you. Follow the ledge around to find a Page ([item=206453]).
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• Credit to Perridan for this one. A Page ([item=206450]) is sitting on the very bottom of the slime tunnel between Construct and Arachnid quarters, on the Construct side.

Military Quarter:

• [item=206473] required. Another grappling point is in Razuvius' room, just before the ramp down to fight him, up on a small ledge. After grappling up, if you run allllllllll the way around back the way you came (eastward over the stables) there's another Lost Page ([item=206464]?) at the end of the ledge. You can actually see the Page on the balcony as you're coming in, but you can't get to it without grappling. Interestingly, you can't follow the path around the other way (over Razuvius) as there's an invisible wall.
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• [item=206473] required. Credit again to Strath: Just after coming down from the ramp after Razuvius, there's a grapple point up on the high ledge to the left. It can hide behind banners so it takes some looking. You'll need to follow the ledge a long way around the room until you're above the entrance of Gothik's, and you'll find a Page ([item=206462]) there.
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• One page is sitting in one of the alcoves in the floating weapons room in the Military Quarter just before Gothik. It's the tall alcove one on the southeast side of the room. The Page ([item=206465]) is just sitting there.
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• Turn left just as you enter the Four Horsemen's room, and go for the green slime alcove in the wall. Another Page ([item=206463]) is sitting on the right of the slime stream.

Construct Quarter: ([item=206473] required for all.)

• The first one (progressing through) is in Grobbulus' room. When you get up to the top platform, turn to face the room at large and look at the lip running along the length of the room. There's a hook off to the right (from this vantage point), above and to the side of the ramps. You follow the lip around to one of the Lost Pages ([item=206455]?).
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• There's one visible as you go from Grobbulus to Gluth, on a flat platform across from the walking pipe while you cross over the wing entry room. It leads to one of the Lost Pages ([item=206454]?).
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• There's a series of them leading from the pipe just before Gluth. Spot it to the left in the hole you can fall through, then turn around once you grapple to it. Another page ([item=206456]?) at the end of the grappling + jumping series. You'll need to run along the pipes for some jumps and some grapples.
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• Another series of grapples is in Thaddius' room on the hanging platforms. You start the chain from the southwest (Stalagg's) platform, up to the left on the platform jutting out from the wall. You can use either one up there (there's 2), but you'll want to end up on the westmost one (right one as you're facing the wall). Then look for the hook to get over to a platform away from the wall. Then another platform adjacent to that one (still away from the wall) closer to the southern side of the room, closer to the entrance. Then turn around and look way up into the weird green alcoves. There's a grapple point way up there.There's another page ([item=206457]?) when you get up there.
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There is also now a Wowhead guide with picture references here.

All the edits have been to increase info, reorder, or clarify.

Not ONE PERSON has bothered to mention where to hand the pages in to! Take the pages to Master craftsman Omarion in Light's Hope Chapel. He's inside the alter building.

I hope this helps everyone while looking for the pages for Putting Wilhelm Out of Business:

Arachnid Quarter
[item=206451] 1st Room in the Arachnid Quarter inside the broken green pillar on the ground
[item=206452] In the Tunnel with the Spider Eggs linking Grand Widow Faerlina to Maexxna, on the right side (southern side) between the Spidereggs
[item=206453] In Maexxnas's Nest, over the entrance is a hook point, follow the ledge to the right and you will find the page on the ground

Construct Quarter
[item=206454] After Grobbulus before entering the drainage tube which leads to Gluth, while standing on the pipe look to your left on the ledge above the door is a grapple point, right next to it on the ground are the pages
[item=206455] In Grobbulus room, go up the ramp and turn back into the room. On the right side wall [east] there is a ledge, on top of this ledge is a Grapplepoint. Follow the Ledge and at the end are the pages.
[item=206456] In the Broken Drainage Pipe leading from Grobbulus to Gluth look through the broken parts and to your left. On top of the Pipe is a Grapple point the next point is on the pipe you just exited through the broken hole after that you continue from pipe to pipe up north. The Pages are on the most northern Pipe.
[item=206457] In "The Halls of Reanimation"-Room use the hooks on the way to the Dead NPC Zackett Skullsmash, the Pages are right next to the hook on the highest level.

Military Quarter
[item=206464] In the Room with Instructor Razuvios, just in front of the ramp leading down towards the boss is a hook point, follow the ledge to the right and you will find the Pages at the end of the ledge.
[item=206462] Just after the Razuvios Bossfight when entering the room with the floating weapon mobs is a ledge right above the room entrances left corner there is a grappling point between the first and second blue ribbon just above one square shape on the wall. Follow the ledge and the pages will be on ledge above the entrance to Gothik's bossroom.
[item=206465] In the Room after Razuvios [the same room as Page 25 & 26] on the southeastern wall there is a carriage with crates behind it. To the right of the crates are rectangular shapes on the wall and a blue rippon. The Pages are in the shape to the right of the ribbon.
[item=206463] In "The Horsemen's Assembly" in the green slime alcove in the eastern corner (just left of the entrance) of the bossroom.

Plague Quarter
[item=206458] In the first room of the Plague Quarter on the left side is a Meatwagon, on its center wheel are the pages.
[item=206459] In the Hallway filled with Mushrooms, on th left side next to the slimepit with the grate on top. THere is a red mushroom to the northwest of it, the Pages are on top of it.
[item=206460] In "The Necrotic Vaul" in the Northern locked Gate on the ground.

Outer Ring
[item=206450] In the slime tunnel between Arachnid and Construct Quarters, the Pages are on the ground under"water".
[item=206461] In the Outer Ring section of the Plague Quarter is an entry to Noth's bossroom. The Pages are just on the edge of the platform.

There is also a guide with pictures but I didn't see it early enough so since I wrote this already... I wanted to post this anyway :D